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New model of inner Earth clarifies mantle motion

Written by: Staff

Washington, May 2 : Scientists have developed a new model of inner Earth, which pulls past information and hypotheses into a coherent story to clarify mantle motion.

Ed Garnero, seismologist and an associate professor in Arizona State University's (ASU) School of Earth and Space Exploration, along with colleagues, has developed the model.

The mantle, which is the thick layer of silicate rock surrounding the dense, iron-nickel core, is below the Earth's crust.

It is subdivided into the upper and lower mantle, extending to a depth of about 2,900 km (1,800 miles).

According to Garnero, "The past maybe two or three years there have been a lot of papers in Science and Nature about the deep mantle from seismologists and mineral physicists and it's getting really confusing because there are contradictions amongst the different papers." "But we've discovered that there is a single framework that is compatible with all these different findings," he added.

Garnero partnered with geodynamicist and assistant professor Allen McNamara, also in the School of Earth and Space Exploration in ASU's College of Liberal Arts and Sciences, to synthesize the information for their paper.

According to the ASU scientists, all this recent research of the past few years fits into a single story.

The pair paints a story for a chemically complex inner earth, a model that sharply contrasts the heavily relied upon paradigm of the past few decades that the mantle is all one thing and well mixed.

The original model was composed of simple concentric spheres representing the core, mantle and crust - but the inner Earth isn't that simple.

Garnero and McNamara's framework is based upon the assumption that the Earth's mantle is not isochemical (chemically homogenous made entirely of only one kind of material).

According to Garnero, new data supports a mantle that consists of more than one type of material.

Observations, modeling and predictions have shown that the deepest mantle is complex and significantly more anomalous than the rest of the lower mantle.

To understand this region, seismologists analyze tomographic images constructed from seismic wave readings. For 25 years, they have been detecting differences in the speeds of waves that go through the mantle.

This difference in wave speeds provides an "intangible map" of the major boundaries inside the mantle - where hot areas are, where cold areas are, where there are regions that might be a different composition, etc.

If the mantle is all the same material, then researchers shouldn't be observing the boundary between hot and cold in the mantle as a super sharp edge and the temperature anomalies should also be more spread out.

According to McNamara, "We observe the motions of plate tectonics very well, but we can't fully understand how the mantle is causing these motions until we better understand how the mantle itself is convecting."


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